In modern electronic systems, DRAM memories or flash memories are often used as nonvolatile memories. Although flash memory technology has undergone scaling into the range below 100 nm in recent years, the disadvantages of these memory technologies, such as long write/erase times, which typically lie in the milliseconds range, high write voltages, which typically lie in the range of 10 to 13 V, and accordingly require high programming energies, and also the limited number of read and write cycles, have heretofore not been solved satisfactorily. Furthermore, it must be assumed that, on account of their memory mechanism based on the storage of charge, even these memory technologies will encounter their scaling limits in the foreseeable future. Furthermore, the fabrication method in particular for flash memory cells is costly and comparatively complex.
By contrast, memory components based on resistive memory cells, in particular so-called CBRAM (conductive bridging RAM) memory cells or solid electrolyte memory cells, represent a new and promising technology for semiconductor-based memory components. With this type of memory components, a resistive memory cell can be switched by electrical pulses between a high-resistance state (“OFF” state) and a low-resistance state (“ON” state), as a result of which one information unit (bit) can be stored.
In concrete terms, the memory element of a resistive CBRAM memory cell is typically constructed from an inert electrode, a reactive electrode, and also a highly resistive—but conductive for ions—carrier material (solid electrolyte) arranged between these two electrodes. The two electrodes form together with the solid electrolyte a redox system in which a redox reaction proceeds above a defined threshold voltage. Depending on the polarity of a voltage applied to the two electrodes, which must be greater than the threshold voltage, the redox reaction can proceed in one reaction direction or the other, metal ions being produced or discharged. Metal ions produced at the reactive electrode are reduced in the solid electrolyte and form metallic precipitates which increase in their number and size until a low-resistance metallic current path bridging the two electrodes finally forms. In this state, the electrical resistance of the solid electrolyte is reduced significantly, for instance by several orders of magnitude, compared with the high-resistance OFF state without such a low-resistance current path, whereby the ON state of the CBRAM memory cell is defined.
In particular, chalcogenides, which are alloys containing chalcogens (elements of main group VI of the periodic table), have been investigated with regard to their suitability as a carrier material, and it has been shown that these alloys have particularly good switching properties.
More precise investigations of the metallic current path bridging the two electrodes have shown that usually a plurality of autonomous metallic bridges are formed between the two electrodes. This has the effect, however, that these bridges in each case have to be resolved again during the erase operation (by application of a voltage of opposite polarity to that when writing to or programming the memory cell), that is to say that the metallic precipitants of the metallic bridges have to be oxidized to form metal ions and electrons. For this reason, a comparatively long period of time is disadvantageously required until the resistive memory element of the memory cell can assume its high-resistance (OFF) state again without metallic bridges between the electrodes, that is to say the resistive memory cell can be erased. While the programming operation is effected in the nanoseconds range, substantially longer time periods are required for the erase process for this reason. No precautions or methods that can bring about a solution to this problem have as yet been disclosed heretofore.